The present invention to a hand power tool with a turnable base plate.
More particularly, it relates to a motor driven hand power tool for separating works,especially a hand circular saw with a height adjustment for selecting a cutting depth and a cutting element movable about a turning axis and fixable in each turning position.
A hand power tool of the above mentioned general type is known in the art. One of such hand power tools is disclosed for example in the German document DE-PS 743,056. It is turnably connected with a base plate through a hinge-like turning-guiding means. The physical turning (or tilting) axle formed by the turning-guiding means is arranged on the base plate so that it is located approximately on the upper surface of the workpiece. Therefore the cutting edges during all turning angle positions of the hand held power tool are approximately congruent and lie in a common line of sight of the cutting edge indicator.
With the above described arrangement it can be achieved when the turning axis extends directly on the workpiece surface in the cutting line between the plane of the base plate-abutment surface and the tool plane, with the tool extending perpendicular to the abutment surface. This was obvious to persons skilled in the art by means of simple geometrical considerations before the present application for the protection. Possibly it was not substantially meaningful to realize or to discuss the approximate solution with physical turning axle. The approximate solution was developed further, and the physical hinge axle was replaced by a non-physical turning axle in form of a coulisse-like turning guiding member. This was developed in 1981 with the wood hand circular saw 2117 t 65 i and 2118 t 85 i. Their coulisse guides form non-physical turning axes extending under the base plate, and the center point of the circular guiding path or cutting line lie between the plane of tile base plate abutment surface and the tool plane. Thereby an accurate coincidence of the cutting edges in all turning angular positions is obtained.
During works with a guiding rail there is the disadvantage that the turning axis extends above the workpiece surface and it is placed in parallel by the thickness of the guiding rail. This disadvantage is shown in the German document DE-OS 3,615,848, without means with which the turning axis must be adjustable with or without the use of the guiding rail.
A further hand circular saw is disclosed in the German document DE-OS 3,445,431 there is an adjusting screw on the side which is opposite to the pivot bearing. The saw blade can be practically turnable about the pivot bearing and transverse to the feed direction in a small angular region by means of the adjusting screw. Thereby the parallel position of the saw blade to the feed direction can be obtained when it assumes an inclined position due to unfavorable tolerance adding. It is provided and assumed that when a parallel deviation of the saw blade from the nominal position is not corrected. None of the hand tools eliminates the above mentioned disadvantageous property.
A further disadvantage is that the separating tool is not adjustable in uncoupled position from the turning axis. Thereby during adjustment of the angular position of the tool it is unavoidable that the position of the tool relative to the turning axis is adjusted so that despite the parallel position of the tool relative to the feed direction, the results of the inclined position of the tool to the turning axis is worse than it was before: parallel displaced cutting joints during changes of the turning angle, inclined cut to the feed direction at turning angle 45.degree., tool contact with the guiding arm. The cutting line of sight thereby cannot be practically determined. In the worse case the separating tool can destroy the guiding rail.
This further disadvantage is avoided in accordance with the solution disclosed in the German document DE-OS 3,243,564. Here a wrapper lip which is mounted with a considerable extension on the guiding rail and acts as a cutting line of sight and chip breaker, is cut during the first cut with the separating tool. Thereby an error compensating pair hand tool/guiding rail can be formed. The error compensation is effective only between the pairs which are fixedly arranged relative to one another, with a low wear, practically only in a new position. It is for example eliminated during the exchange of an old saw blade for a new saw blade with a mass which deviates from the first saw blade. The error during a separation of a error compensating pair can be greater than new hand power tools of the same type with an already "cut" old guiding rail is used: the cutting edge of the rubber lip can be located in an unfavorable case so that, outside the regional pair, neither the function of the guiding rail as a chip breaker nor a cutting line of sight can be provided. This danger is characteristic especially for hand tool operations with several, same-type machines of the same manufacture.
Such errors have been accepted until now. They were not compensatable with efficient expenses and occurred from the power tool to the power tool more or less in the band width of the tolerance play. Thus, for example in hand circular saws a tolerance play of the parallel position of the saw blade is conventionally to be approximately .+-.1 mm. This great tolerance width results from the requirement that individual parts distributed over the mass chain are cost favorable to manufacture and from the assumption that the cost optimization was favorable to the accuracy.